Patients are evenly enrolled into 2 groups based on Tanner Stage. Group I patients are Tanner Stage 1 or 2 (pre-pubertal). Group II patients are Tanner Stage 3, 4, or 5 (pubertal). Each patient receives a single oral dose of abacavir given as the commercially available oral solution. Pharmacokinetic blood samples are collected before dosing and at 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4, 6, and 8 hours post dose for abacavir concentrations.